Furnace wall with finned wall tubes



March 2, 1954 A. HUET 2.670.722

FURNACE WALL WITH FINNED WALL TUBES Filed April 28, 1951 34 35 36 TTE- //VD/PE /l/ET IN VEN TOR.

HT ORI/EY Patented Mar. 2, 17954 UNITED s'rAras est am o-F'Frea L 'llhisiinventionarelates toxz'ombustionfchambers,` ofi-boileraforexample-Which;mayffunction under pressure: andi more *f particularly: to theprovision'- of" af, gasA tight. combustion; chamber enclosed by" walls lmadei Without. refractory material' or with very littlefrefractory materiali Gombustion chambers; with :water cooled: tubes lining the walls` arezfwell known;

Water tubes located along the lateral-.walls of aicombustionchamber are; exposed tor radiation whichi isili-ot;` th'efsame on; all( the .surfaces of the. tubes.. Thus; it.; is. thattl. normally the front'. sur.:-V face.:I on af, tuba`v being. directedf towardy the iirey spaceisexposedatosgreaten caloric radiationthan theT back; Surfacezwhich is. directed toward the heatreceived by theffront face of thectubeffacing. towardithe `lireaspacefandbytherear f aceidirected toward theA wall: of thecombustion chamber is:

compensated for by providing,- oni its.I rear face lateralf proj ectionsv or nswhich; have-` the effect of..increasing. the surfacel of thetube exposed: to

the radiant heat. Thesanspermitthe accumulationsonzthei rean faca of: the i tube of.- an amount of` heat equal. to -that which is; received-.by the front `fac-esofthatfthey;are at the-same tempera-A turefor near-,1yr so.

A. corollary. oft, this yfeature of` the invention. is

that the. ns.- on the: rear face of the. tube are slightly c urvedfconvexly.` Withfrespect to the furnace space so,that. these ns which.. are themselizesisubjected to.a..diierenc.e ofgcaloric radiation-on theirrdorsal faceandfon their ventral face may;y correct. fr thef effect. of .the differences of expansionswhich resulttherefrom and. reach the maximum lvelin' service. The, junction of the nnswith. the surface..ofl'the tube. is thickened so tliatnostressdueto their differences .of expansion isl transmitted.. to4 the. norm'a1` wall thickness of tliebasetube. which thus wholly retains its resistance.. td` distortion Thisl thickness', at the; rootalso assure'sa' better distribution of the? heat ongtlieiwliole'circumference-of'thetube; and gives"v italargemoment ofinertia'to resist" mechanical stresses:

According to another' feature" ofI the present' invention; such nned" tubesbeing exposed to radiationhave"'b'ehindlctlieJ nsrat tight Wall i made up= of 'ironA plates off thei desired thickness* andvx made' of La-serlies of secondary laterali-fins oitlB- back oit eaoh tube, these!fnsabuttingfalong tli'cirl longitudinaliside! faces 'andbeingl welded tgTethe-ifto form a Wall; In other wordsthe! vvat'eritu-lces'` comprise. in a measure, completely-` or'partia1ll5r,ai.. f ramework! on which there: are fast'en'edl,r possiblly/ with insulation, thevcorrugatedliron platesWillian?.A form the tight envelope ofV the? combustioni cham.- ber.

Theadvantage of1 this arrangementvfi's'that the? iinned: tubes. form water screens and protect their sheet metal wallv from: radiation;w Thisias'sures'i maintenance of:` the tightness: ofrthef combustionchamber which. makes; it'possible toi. enclose-thisiv chamber with less thick iron-plates; andto provide:

only a little or no refractory materialY fonr` tlie;y

chamber. Furthermore-the'heatfabsorbedzbythet sheet iron Wallv is retransmitted by conductivity:- to the. Water tubesonto; which the-.ironiplatesfwhich make up said walls are; fastened.

Corrugations are advantageously' providedi oni the sheet iron blades preferably extendinginitwo: directions (longitudinally and transversely-)H soffasf` to absorb the expansion diiferences whilejstiien-L ingvthef Whole of, the Wallagainstftheby inner.i pressure.- and` the :possible deformations.

Figure 1f is a cross,4 sectional viewf of aportionaof a gas-tight combustionfchamber-wallxlinednwithi water tubes; according to fthe .inventionsv Figure 2 shows; in.A elevationi-Withipartialfr I: movalof the 'watertubess affragmentof-said-.wall.

Figure 3 isaY crossesectionalf. viewfy ofL` af. tubefa with tapering rearnswhich are thicker atltheirfa combustionchamber. 'I'.hefront face ilA o# the tube which is directedtowardth'e iirespacefA issubjected to the-actionof radiant lieatzexlf erted-.in thel directionoi the arrovvs A.- Thebaclc face*` I3., of thetube faces towardthe Wallr 12a and" thusl` is subjectedfto radiant heatfvrelected rOm'said wall in :the:directionofV arrows-32B. Nor--r mally, .the-amount of; heat radiatc'edibyy| reiiectiom from thenwall. l2* is less, thanithat1whichis diatedli directly from the nrespacez CfonseezY tween the two faces II, I3 which produces differences in the expansions and distortions of the tube.

To correct this disadvantage in accordance with this invention, the rear face I3 of tube I0 which faces toward the Wall I2 is equipped,

for example, with two lateral fins I5, I6. These fins are joined by a quite thick root I'I to the wall of the tube, and are preferably curved concavely with respect to the furnace as shown in Fig. l. The over-al1 surface of tube II) exposed to the radiation of wall I2 is thus increased, and the surface of the ns is calculated in such a Way that the heat received by these ns along arrows B and C brings the rear and side faces o! the tube to approximately the same temperature as the front face II that is subjected directly to the radiation A coming from the fire space.

On the tube 20 of Figure 3 the fins 2I, 22 decrease in thickness towards a point I8 approxmately` at the center part of the back of the tube, the point I8 being in a plane that contains the longitudinal axis of the tube, which plane is normal to the tube wall, so as to obtain a more uniform temperature gradient in the fins and the face of the tube onto which they are bonded or with which they are integral.

According to the invention, the ns I5, I6 or 2l, 22 of the tubes IIi or 2U are concave-convex. The front concave faces of the fins, being directed toward the iire space thus receive more radiant heat and expand more than the back of the tins subjected to the heat reiiected by the wall I2 in the direction of arrows B. The difference of the expansions of the two faces of the ns has the effect of rectifying the concavity of the ns, as is shown in Fig. 4, in which the fins become practically planar at maximum expansion when they are in service. This convexity of the ns also assures that the side faces of the tube not subjected to the intense direct radiation receive a contribution of indirect ra diation D.

It will be noted that the root of the iin, that is to say, the surface along which it is joined to the cylindrical periphery of the tube is sufficiently broad so that the expansion stresses to which the ns are subjected are not transmitted to the wall proper of the tube.

These tubes With ns can be made either by a suitable welding of the fins onto the surface of the tubes, or in the "solid-forged (mono block) form, that is, the fins and the tube are produced in one single piece.

As may be seen in Fig. l the combustion chamber which is assumed to operate under pressure has along its wall a lining of Water tubes each one having ns I5, I6 which are exposed to the radiation from the chamber, and which, by the effect of the expansions due to the temperature elevation, are thereby brought in contact, or almost so, along their longitudinal edges as shown in dotted lines in Fig. l. In this Way these ns I5, I6 protect the wall I2 located behind them from radiation.

According to a further feature of the Present invention, the gas tight Wall of the combustion chamber may be made up of corrugated iron plate 3B which is preferably fastened onto the F back of the tubes III between ns I5, I6. This fastening can be made either by continuous welding, or by spot welding, or also by dowels or pins fastened onto the tubes ID' and penetrating the sheet iron with exterior screws, or

by collars which are unitary with the sheet iron 30 and which girdle the tubes I0 with possible interposition of an insulating material. The plate 30 is preferably corrugated in both directions, longitudinally at 3| and transversely at 32 as shown in Fig. 5 so as to absorb the differences of expansion and the possible deformations, while stiffening the Whole of the Wall against the inner pressure of the combustion chamber.

Wall I2 may be made with the aid of elements already fastened at 33 to the rear faces of tubes I0 in the manner of a secondary pair of ns 34, 35. The edges 36 of these fins on adjacent tubes are welded in continuous fashion on their entire length to form, as shown in Fig. 2, a con- -tinuous wall enclosing the combustion chamber.

The protection against radiation afforded by the ns of the tubes IB or 20 makes it possible to make wall I2 with relatively thin iron plates, and the heat-insulating layer usually provided on the outside all around the combustion chamber may be of a relatively reduced thickness, and possibly even eliminated. The expansion differences which are produced by the effect of the temperature variations in the fins I5, I6 or 2i, 22 may make it necessary to provide slits interrupting the length of these fins.

What is claim is:

l. In a heat exchanger having parallel metallic tubes lining the Wall of a combustion chamber or the like in which the tubes are exposed to radiation; a pair of longitudinally extending metallic iins on the rear Iface of each tube confronting the furnace wall and projecting laterally in opposite directions beyond each side of the tube, said iins each being conoavo-convex in transverse cross-section and curving toward the front face of the tube and being thinner at their distal ends than at their root junctions with the tube so that upon exposure to heat the ns expand and their concave and convex surfaces tend to become planar while their distal ends move rearwardly so as to substantially close the gaps between the longitudinal edges of adjacent fins on adjacent tubes.

2. In a heat exchanger having parallel metallic tubes lining the wall of a combustion chamber or the like in which the tubes are exposed to radiation; a pair of longitudinally extending metallic fins projecting laterally in opposite directions from the face of each tube that confronts the furnace wall, said fins being concave-convex in transverse cross-section and curving toward the front face of the tube and tapering from their root junctions with the tube to their distal ends so that upon exposure to heat the ns expand and tend to pivot rearwardly on the tube so as to substantially close the gaps between the longitudinal edges of adjacent fins on adjacent tubes.

3. In a heat exchanger having parallel metallic tubes lining the wall of a combustion chamber or the like in which the tubes are exposed to radiation; a pair of longitudinal metallic :fins extending across the rear face of each tube that confronts the furnace wall and projecting laterally in opposite directions beyond each side of the tube, said ns being concave-convex in transverse cross-section and curving toward the front face of the tube and tapering from their root junctions with the tube to their distal ends with the two fins merging in a reduced root section located in a plane that contains the longitudinal axis of the tube and which is normal to the furnace wall so that upon expansion under heat the 5 concave and convex surfaces 0f the ns tend to Number become planar so as to substantially close the 2,148,484 gaps between the longitudinal edges oi.' adjacent 2,248,890 fins on adjacent tubes. 2,304,788

ANDRE HUET'. 5

References cited in the 111e of this patent m1111383;

UNITED STATES PATENTS 9 Number Name Date 10 1,774,150 vMurray Aug. 26, 1930 Name Date Lucke Feb. 28, 1939 Murray July 8, 1941 Bailey Dec. 15, 1942 FOREIGN PATENTS Country Date Netherlands Nov. 15, 1928 

